U.S. Pat. Nos. 4,503,102 and 4,521,437 disclose the preparation of a polyethylene film for use in the manufacture of a disposable pouch for packaging of liquids such as milk. U.S. Pat. No. 4,503,102 discloses pouches made from a blend of a linear ethylene copolymer copolymerized from ethylene and an alpha-olefin at the C.sub.4 -C.sub.10 range and an ethylene-vinyl acetate polymer copolymerized from ethylene and vinyl acetate. The linear polyethylene copolymer has a density of from 0.916 to 0.930 grams/cubic centimeter (g/cm.sup.3) and a melt index of from 0.3 to 2.0 grams/10 minutes (g/10 min). The ethylene-vinyl acetate polymer has a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10 g/10 min. The blend disclosed in U.S. Pat. No. 4,503,102 has a weight ratio of linear low density polyethylene to ethylene-vinyl acetate polymer of from 1.2:1 to 4:1. U.S. Pat. No. 4,503,102 also discloses laminates having as a sealant film the aforementioned blend.
U.S. Pat. No. 4,521,437 describes pouches made from a sealant film which is from 50 to 100 parts of a linear copolymer of ethylene and octene-1 having a density of from 0.916 to 0.930 g/cm.sup.3 and a melt index of 0.3 to 2.0 g/10 min and from 0 to 50 parts by weight of at least one polymer selected from the group consisting of a linear copolymer of ethylene and a C.sub.1 -C.sub.10 alpha-olefin having a density of from 0.916 to 0.930 g/cm.sup.3 and a melt index of from 0.3 to 2.0 g/10 min, a high-pressure polyethylene having a density of from 0.916 to 0.924 g/cm.sup.3 and a melt index of from 1 to 10 g/10 min and blends thereof. The sealant film disclosed in the U.S. Pat. No. 4,521,437 is selected on the basis of providing (a) pouches with an M-test value substantially smaller, at the same film thickness, than that obtained for pouches made with film of a blend of 85 parts of a linear ethylene/butene-1 copolymer having a density of about 0.919 g/cm.sup.3 and a melt index of about 0.75 g/10 min and 15 parts of a high pressure polyethylene having a density of about 0.918 g/cm.sup.3 and a melt index of 8.5 g/10 min, or (b) an M(2)-test value of less than about 12%, for pouches having a volume of from greater than 1.3 to 5 liters, or (c) an M(1.3)-test value of less than about 5% for pouches having a volume of from 0.1 to 1.3 liters. The M, M(2) and M(1.3)-tests are defined pouch drop tests in U.S. Pat. No. 4,521,437. The pouches may also be made from composite films in which the sealant film forms at least the inner layer.
The polyethylene pouches known in the prior art have some deficiencies. The problems associated with the prior art known films relate to the sealing properties and performance properties of the film for preparing pouches. In particular, prior art films made into pouches have a high incident of "leakers", i.e., seal defects such as pinholes which develop at or near the seal in which flowable material, for example milk, escapes from the pouch. Although the seal and performance properties of the prior art films have been satisfactory, there is still a need in the industry for better seal and performance properties in films for manufacture of hermetically sealed pouches containing flowable materials. More particularly, there is a need for improved sealing properties of the film such as hot tack and heat seal initiation temperature in order to improve the processability of the film and to improve pouches made from the films.
For example, the line speed of known packaging equipment used for manufacturing pouches such as form, fill anti seal machines, is currently limited by the sealing properties of the film used in the machines. Prior art polyethylene films have high hot tack seal initiation temperatures and a narrow sealing range. Therefore, the rate at which a form, fill and seal machine can produce pouches is limited. If the heat seal temperature range where one could obtain strong seals is broadened, then the speed of a form, fill and seal machine can be increased and, thus, the rate at which pouches can be produced can be increased. Until the present invention, many have attempted to broaden the heat seal temperature range of pouch film without success.
It is desired to provide a polyethylene film structure for a pouch container having a broad heat sealing range with performance properties as good or better than the known prior art pouch films.
It is also desired to provide a film structure for a pouch container having a heat seal layer such that the film structure has a broader sealing range for pouch conversion and has acceptable physical properties in the finished product.
It is further desired to provide a pouch made from the aforementioned film structures such that the pouch has a reduced failure rate.